Thank you all for your help.
My conclusions are:
- utf8 is not so generalized that I did hope, certainly for 2 reasons, the weight of the past and all lines of code soon written. And certainly too because it is more a problem for non speaking english people.
- there is not default utf8 at global perl level (and it could be dangerous)
- an excellent default at scope level, and then at script level is:

use utf8::all
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